The present invention relates generally to RF filters and more particularly to optical RF bandpass filters.
In my U.S. Pat. No. 4,577,924, an optical RF bandpass filter was described which consisted of a multimode optical fiber segment having reflecting mirrors on each end so that it functioned as a resonant cavity with respect to a particular modulation frequency when the length of the fiber was equal to one half of the modulation wavelength of the light injected into the fiber. This type of filter can advantageously be used in many application for controlling or selecting frequencies transmitted, for example in electronic intelligence receivers, data busses, fast frequency hopping modems, and other signal processing applications.
My U.S. Pat. No. 4,726,644 described a fiber optic data bus and discussed coupling a pair of optical bandpass filters in series or cascade to produce a narrower passband. However, such cascade arrangements may result in significant insertion losses as a result of back reflections.